An image forming apparatus using an electrophotographic system performs an initial process (initializing process).
The initial process means a process of maintaining image quality in order to make image density appropriate, a process of checking the amount of toner or the amount of waste toner, or the like. When the image forming apparatus is a color machine, the initial process includes a registration process of registering positions of respective colors.
At the time of start-up, the image forming apparatus performs the initial process. Alternatively, after the image forming apparatus prints and outputs several thousand sheets, or after the image forming apparatus is left for a while, the image forming apparatus performs the initial process.
The image forming apparatus performs fixation heating. The fixation heating means raising the respective surface temperatures of a heat roller and a press roller in a fixing unit to printable fixing temperatures.
In the heating process, heat from a heat source is conducted to the heat roller and the press roller, and the temperature of the fixing unit is raised. A time required for the fixation heating is long. The time occupies a large ratio in the time required for the start-up process of the whole image forming apparatus. The power consumption by the fixing unit is largest in the image forming apparatus.
Hitherto, the image forming apparatus performs the initial process at the same time as the fixation heating. At the time of start-up, the image forming apparatus performs both the initial process and the fixation heating.
However, the total amount of power supplied from a commercial power source to the image forming apparatus is limited. The sum of the total amount of power required to perform the initial process and the total amount of power required for the fixation heating is limited.
When the initial process is performed, the image forming apparatus can not distribute a sufficient amount of power required for the fixation heating to the fixing unit. At the time of start-up operation, the image forming apparatus can not supply a sufficient amount of power to the fixing unit.
In order to raise the respective roller temperatures to specified temperatures by power of an amount distributed by a power source part, the image forming apparatus requires a longer heating time.
When the image forming apparatus requires the long time for heating the fixing unit, delay occurs in turning the state of the image forming apparatus from the state of the initial process to a printable state.
In the image forming apparatus, when the power source is turned on, or after several thousand sheets are printed and outputted, or at the time of resuming after the apparatus is left, delay occurs in the originally expected return time of the image forming apparatus.